There is a need for longitudinal studies of twins in which there is direct behavioral assessment of multidimensional language abilities during the preschool period followed by direct behavioral assessment of multidimensional language abilities and early reading skills during the early elementary school years. This project builds on an existing program of investigation that has recruited and obtained behavioral assessments on 702 twin pairs, and 237 single born children, ages 2-6 years. Family members are recruited for behavioral assessment, and extensive family, home, and child information has been obtained via questionnaires. This proposal will extend the longitudinal data to cover 2-9 years, in order to obtain heritability and environmentality estimates for the transition from early language to later reading abilities. Of particular interest are the genetic and environmental influences on the condition of Specific Language Impairment and subsequent reading impairments in young children, the language phenotypes, and indications of age-related modulations of genetic and environmental effects. Initial molecular studies will test for linkage of SLI phenotypes to candidate regions that have been identified for SLI and reading disability. The outcomes will be highly relevant for the identification of children at risk for language disability and the estimation of possible genetic, environmental, and interactive age modulated effects on language and reading acquisition.